Methods of this type and corresponding apparatus have long been known from the prior art. The disclosure further relates to an apparatus for blow moulding containers from a thermoplastic material, in which a compressor produces compressed air in the stretch blow moulding machine, this compressed air being used for the use of pneumatic consumer devices and/or also for shaping the plastics material pre-forms into the containers.
A blow moulding method of producing hollow bodies from plastics material, as well as an apparatus and an installation for performing this method are provided by DE 20 2005 020 679 U1.
In this case a crucial problem in the case of this shaping is the high consumption of compressed air of stretch blow moulding machines of this type. It is usual for the compressed air to be produced by way of an external compressor, this compressor generally producing a pressure of up to 40 bar and this high pressure level then being supplied to the stretch blow moulding machine. In the machine itself this pressure is then reduced to the required pressures, for example for pre-blowing or for final-blowing the plastics material containers. In this way, for example, a first pressure level can be between 6 and 25 bar and a second pressure level between 25 and 40 bar. In addition, a pressure of constantly 10 bar is required for the control valves of the apparatus, in which case this pressure can also be less depending upon the valves.
To a certain extent a streching rod also moves into the container in a pneumatic manner during the shaping, in order to assist the shaping process. In this case the corresponding pneumatic cylinder has a pressure level of 8 bar while moving in and a pressure of from 3 to 8 bar while moving out.
It may be desirable to make available a method and an apparatus by which the energy consumption for the compressed air supply is reduced.